Vitamin D is known to play an important role in bone metabolism through regulation of calcium and phosphate homeostasis and may also play an important role in immune system regulation. Rickets secondary to&nbspvitamin D deficiency&nbspoccurs as a result of decreased sunlight exposure and low vitamin D intake. The result is poor bone growth, soft and deformed bones, and possible retardation in severe cases. Some children develop potentially&nbsplife-threatening hypocalcaemia. Nutritional rickets almost disappeared with the recognition of the preventive role of sunlight and Vitamin D fortification of infant formulas and milk.

During the past 20 years, however, there has been an increase in the published reports of nutritional rickets. Those most at risk include breastfed infants with darker skin colour and others with&nbsplimited exposure to sunlight.

Sources of Vitamin D

Vitamin D is found in very few foods naturally, such as fish liver oil, fatty fish, and egg yolk. It is added to cow's milk, infant formula, some bread and cereals, and some juices. Both infant formula and milk are fortified with 400 IU of vitamin D per quart.

Vitamin D is synthesised in the skin by the action of ultraviolet light from the sun on a cholesterol precursor. However, sunlight-mediated synthesis of vitamin D in the skin is profoundly affected by a wide variety of factors including:

Those who do not get enough sunlight exposure to their skin, stay indoors, or live in smoggy areas

Those who consume little, if any, vitamin D fortified milk

Those who eat a strict vegan diet (avoiding all animal products including milk and eggs)

Those who have deeply pigmented skin

Are breastfed and do not take vitamin D supplements

Dermatologists&nbspand&nbspcancer experts&nbspadvise caution in exposure to sun (or to sunlight), especially in childhood, and recommend regular use of sunscreens. Sunscreens markedly decrease vitamin D production in the skin. In Northern India, the sun is too weak to allow the skin to synthesise vitamin D during the winter months.

Breastfeeding and Vitamin D

Breast milk is the best source of nutrition for infants. Breast milk contains some highly bio-available vitamin D, but the amount of vitamin D available in breast milk varies in individuals. Vitamin D in breast milk was intended, by nature, to be a supplement to the amount made by the skin of infants who are routinely exposed to adequate sunlight.